Immunocytochemical localization of gonadotropin-releasing hormone (GnRH) and neuropeptides implicated to be modulating substances for release of GnRH will be visualized in the hypothalamus and median eminence of rats and mice. Initial studies are intended to establish consistent and specific staining for GnRH using the pre-embedding immunocytochemical method. Specificity of the reaction will be determined by immunoabsorption of antisera to GnRH with C-terminal and N-terminal fragments, and intact GnRH. The regional distribution of GnRH neurons and their processes will be determined in serial-sectioned rat brains. The subcellular localization for GnRH neurons during states of synthesis and secretion will be studied before and after the administration of prostaglandin E2. The extrahypothalamic innervation of GnRH projections to various brain areas will be determined; and receptors for GnRH on target neurons will be confirmed using ultrastructural autoradiography after the interventricular injection of monoiodinated GnRH. Finally, double-staining immunocytochemical techniques for the simultaneous demonstration for two antigens on the same section will be developed for the ultrastructural visualization of dopamine-B-hydroxylase and GnRH, as well as for vasopressin and GnRH so that synaptic interrelationships can be established for noradrenergic and vasopressinergic terminals on GnRH cells and fibers.